1. The Field of the Invention
The present invention relates generally to C-arm support structure and a method for mounting the same, and more particularly to a support arm which is slidably mounted to the back of a C-arm at a point of attachment which forms a horizontal line with a center of curvature of the C-arm.
2. The Background Art
It is often desirable to take X-rays of a patient from a number of different positions, preferably without the need for frequent repositioning of the patient. It is preferable that the X-ray support structure not unduly encumber the space immediately surrounding the patient to enable a physician to treat or otherwise attend to the patient without the need to repeatedly remove and replace the X-ray equipment. Mobile C-arm X-ray diagnostic equipment has been developed to meet these needs and has become well known in the medical art of surgical and other interventional procedures.
A C-arm refers generally to an elongate C-shaped member terminating in opposing distal ends of the "C" shape. An X-ray source and an image receptor are typically mounted at or near the distal ends, respectively, of the C-arm in opposing orientation, with the C-arm supported in a suspended position. The space within the C-shape of the arm provides room for the physician to attend to the patient substantially free of interference from the X-ray support structure. The support structure usually rests upon wheels which enable the C-arm to be wheeled from room to room, and along the length of a patient while the physician operates or examines, ensuring that devices such as cardiac catheters, long bone nails, etc. are properly positioned during the procedure.
The C-arm is usually mounted so as to enable rotational movement of the arm in two degrees of freedom, i.e. about two perpendicular axes in a spherical motion. More specifically, the C-arm is slidably mounted to the support structure to enable orbiting rotational movement of the C-arm about its center of curvature, thereby permitting the X-ray source and the image receptor to be selectively oriented vertically, horizontally, or somewhere in between. The C-arm is also laterally rotatable, i.e. in a perpendicular direction relative to the orbiting direction to enable selectively adjustable positioning of the X-ray source and receptor relative to both the width and length of the patient. The spherically rotational aspects of C-arm apparatus allow the physician to take X-rays of the patient at an optimal angle as determined with respect to the particular anatomical condition being imaged.
Designers and manufacturers of C-arm equipment are faced with a number of challenges. The support structure used to support and rotate a C-arm in its various suspended positions must be strong enough to withstand tremendous torsional, tensile and compressive stresses. The support structure must also be heavy enough and have a large enough footprint to avoid tipping over upon lateral rotation of the C-arm, which causes the center of gravity to shift dramatically. There have been previous attempts to provide C-arm support structure to solve the problems mentioned above. Exemplary of such prior art attempts is U.S. Pat. No. 4,955,046 (issued to Siczek et al. on Sep. 4, 1990) which discloses a C-arm apparatus. A wheeled support cart includes a rotatable L-arm upon which a C-arm is slidably mounted. The L-arm thus provides rotational movement of the C-arm in two degrees of freedom.
The prior art C-arm apparatuses such as that disclosed in the U.S. Pat. No. '046 Siczek et al. patent, while useful, are characterized by a number of disadvantages. The mounting structure of the image receptor often encumbers the adjacent sides and/or back convex portion of the C-arm, thereby preventing the main support structure from slidably attaching to that portion of the C-arm. This condition prevents complete horizontal positioning of the image receptor, and necessitates the use of the prior art L-arm. The L-arm attaches to the C-arm at some point below a horizontal extension of the center of curvature of the C-arm, thus permitting the C-arm to slide the image receptor to a horizontal position relative to the center of curvature.
Although the L-arm permits the desired horizontal positioning, it introduces other problems. When the L-arm is rotated, increased lateral moment-arm action is introduced to the system which reduces the system's capacity to avoid tipping. Put another way, the range of motion is reduced and the instability introduced by the L-arm requires a smaller C-arm for given dimensions of the support apparatus. The L-arm itself introduces extra eccentric weight to the system which aggravates the tipping problem. The L-arm design requires sophisticated counter-balancing devices such as is taught in the U.S. Pat. No. '046 Siczek et al. patent. Unpowered C-arm systems have utilized an axis of rotation through the center of mass of the C-arm/L-arm assembly but not through the axis of rotation of the C-arm. High-voltage cables necessary to power the X-ray equipment must be longer in order to traverse the added length of the L-arm, thereby increasing exposed portions of the cables.